This invention relates generally to meltblowing dies. In one aspect the invention relates to a meltblowing die comprising a plurality of self-contained, interchangeable modular units. In another aspect, the invention relates to a modular meltblowing die for meltblowing adhesives onto a substrate.
Meltblowing is a process in which high velocity hot air (normally referred to as "primary air") is used to blow molten fibers extruded from a die onto a collector to form a web, or onto a substrate to form a coating or composite. The process employs a die provided with (a) a plurality of openings (e.g. orifices) formed in the apex of a triangular shaped die tip and (b) flanking air passages. As extruded rows of melt of the polymer melt emerge from the openings, the converging high velocity from air from the air passages contacts the filaments and by drag forces stretches and draws them down forming microsized filaments.
In some meltblowing dies, the openings are in the form of slots. In either design, the die tips are adapted to form a row of filaments which upon contact with the converging sheets of air are carried to and deposited on a collector or a substrate in a random manner.
Meltblowing technology was originally developed for producing nonwoven fabrics but recently has been utilized in the meltblowing of adhesives onto substrates.
In meltblowing adhesives, the filaments are drawn down to their final diameter of 5 to 50.0 microns, preferable 10 to 20.0 microns, and are deposited at random on a substrate to form an adhesive layer thereon onto which may be laminated another layer such as film or other types of materials or fabrics.
In the meltblowing of polymers to form nonwoven fabrics, the polymers, such as polyolefin, particularly polypropylene, are extruded as filaments and drawn down to an average fiber diameter of 0.5 to 10 microns and deposited at random on a collector to form a nonwoven fabric. The integrity of the nonwoven fabric is achieved by fiber entanglement with some fiber-to-fiber fusion. The nonwoven fabrics have many uses including oil wipes, surgical gowns, masks, filters, etc.
The filaments extruded from the die may be continuous or discontinuous. For the purpose of the present invention the term "filament" is used interchangeably with the term "fiber" and refers to both continuous and discontinuous strands.
The meltblowing process grew out of laboratory research by the Naval Research Laboratory which was published in Naval Research Laboratory Report 4364 "Manufacture of Superfine Organic Fibers," Apr. 15, 1954. Exxon Chemical developed a variety of commercial meltblowing dies, processes, and end-use products as evidenced by U.S. Pat. Nos. 3,650,866, 3,704,198, 3,755,527, 3,825,379, 3,849,241, 3,947,537, and 3,978,185 by Beloit and Kimberly Clark. Representative meltblowing patents of these two companies include U.S. Pat. Nos. 3,942,723, 4,100,324, and 4,526,733. More recent meltblowing die improvements are disclosed in U.S. Pat. Nos. 4,818,463 and 4,889,476.
U.S. Pat. No. 5,145,689 discloses dies constructed in side-by-side units with each unit having separate polymer flow systems including internal valves.